You cannot make IQ your only consideration...
First of all, upgrading to any of today's cameras will be a big jump in IQ from your 30D. You'll be going from 8MP to 18MP and from 12 bit to 14 bit (that's an increase from tens of thousands of colors to hundreds of thousands or millions, in case you aren't aware). When I upgraded from 30D to 50D one of the first things that was apparent to me was the cropability of the 50D's images (is cropability a real word? I dunno, but hopefully you get my drift). Where I used to have to fill the 30D's viewfinder with the subject and keep cropping to a minimum, I now could easily change an image from, say, 8x12 horizontal/landscape to 8x12 verical/portrait, with at least as good and often better IQ. That's greater than a 50% crop, yet the 15MP, 14 bit images held together well enough to make excellent prints. I made many a 16x20 or larger from them, too. Also, with the 50D about one stop higher ISO was possible... now using 7D, it's about two stops higher than 30D. With 7D I'll use ISO 3200 without much concern, 6400 with some extra post-processing work. What are your ISO limits with 30D? 800? Maybe 1600 max? Between 7D and the much newer 70D with the slightly higher resolution sensor, IMO the jury is still out but the 70D seems to offer slightly cleaner high ISO images (not enough to make me switch, though).
You will also enjoy some other significant improvements. The rear LCD is bigger and bright enough to be a lot more usable. Self-cleaning sensors can be a biggie, too. My two 7Ds are over four years old and have about 100,000 clicks on each. They have not been pampered in any way, often are used in rather dusty situations. I don't worry much about changing lenses whenever needed, I just use normal precautions. One of my 7Ds has never had a sensor cleaning. The other got it's first cleaning just recently. I can compare that with my old 30Ds, which I found needed a sensor cleaning about every 3 to 6 months at a minimum and often more frequently, shooting the same subjects in the same locations with the same lenses. In other words, the self-cleaning sensors of the newer models (all the ones you mention) really seems to work.
Since you are still using a 30D, you also seem to keep your gear for a while. So durability might be a consideration. I forget exactly, but I think 30D were rated for 100,000 clicks. And I am not entirely sure, haven't seen any Canon statements about it, but I think 70D and 6D probably are too. 7D is rated to 150,000 clicks. I think 5DIII is, too (5DII was). 7D and 5DIII simply "feel" like more pro-oriented cameras. They have more metal construction, 100% viewfinders, and are generally better sealed against dust and moisture (though no Canon DSLR is entirely waterproof!). In fact, a 7D weighs a little more than a full frame 5DII, is only a few grams lighter than the 5DIII. Both 70D and 6D use more plastic, less than 100% viewfinders and are a bit lighter. The 70D has an articulated rear LCD (which can be handy for high an low angle shooting... or video), which makes it a bit thicker and adds some weight. Not that this means they are necessarily much less durable... plastics sometimes survive impacts better than metal. 6D and 70D enjoy 97% and 98% viewfinders, respectively, an improvement compared to the 95% of your 30D.
With any of the newer models you'll see improved AF. The 6D is perhaps the "weakest" of the bunch, but still better than your 30D. The 70D and 7D appear the same, but aren't quite. 7D has a couple focus modes the 70D doesn't, and also uses a discrete chip to run AF (1D series style). However the 70D has a newer and much more powerful processor, and it's got a better/more sophisticated AF Micro Adjust system (something you wouldn't know about yet, coming from 30D... Micro Adjust basically allows you to fine tune AF accuracy for a bunch of your lenses... up to 20 on 7D, up to 40 and better for zooms on 70D). The 5DIII has the most sophisticated AF system of all the cameras you mention, it's actually very similar to the 1DX's AF system (and the 5DIII is priced accordingly). Both the full frame cameras are better able to focus in low light (ratedto -3EV, approx. moonlight), which matches well with thier higher ISO capabilitied. Compare that with -0.5EV rating for your 30D, and -1EV for 7D and 70D.
Still, overall the 7D's or 70D's AF would be a very significant upgrade over what you have now. 30D has a nine-point AF system, with only the center one the more sensitive "dual axis" type. 6D has an eleven-point system, also with only the center one a dual axis (though the remaining ten single axis points will outperform the single axis points in your 30D or even my 5D Mark II). The 7D and 70D both have nineteen AF points, all of which are dual axis type, though the center is still more enhanced "diagonal" type. The 5D Mark III has the most sophisticated AF of all, a 61-point system, up to 41 of which can act as dual axis type.
You also say "subjects are small and far away" and "sports with movement, wildlife with movement". And you cite the 100-400 as a frequently used lens on your 30D, along with 28-135 (among others). This suggests me your emphasis is on longer lenses, telephoto work. If that's the case, you'd likely be best served sticking with a crop sensor camera. For max IQ, you could do better with a FF camera, but you'll have to complement it with considerably more expensive lenses to get the same reach. Instead of your 100-400, you'll need a 600/4 IS, so be prepared to spend upwards of $10,000 US on a lens. You'll also need a rock solid tripod to put it on, since it's nowhere near as portable and handholdable as your current tele-zoom. A quality tripod with a gimbal head will set you back around $1500 US.
Suggesting medium format digital cameras is just plain silly... But the responder's point was that if pure IQ is your only consideration, than those would be the ideal choice. However they'd be terrible choice of camera for what you appear to like to shoot (not to mention incredibly expensive!)
Because of your subjects and the lenses you cited, I'd think a full frame camera wouldn't be the best choice either (unless you just won a lottery and really enjoy lugging around big, heavy gear).
Stick with the crop sensor cameras, I have to strongly recommend.
For your purposes, I think it comes down to a choice between the recently introduced 70D and the four year old 7D. Either would work well for you. In some respects, the 7D is superior. In other ways, the 70D is. The 7D is arguably a more "pro-oriented" camera. It lacks any of the "Scene Modes" you'll find on the Rebel/xxxD and many of the xxD models, including the 70D. Instead the 7D offers three user programmable modes (70D has one). If you are a RAW shooter who regularly post-processes your images, applying your own adjustments, sharpening techniques, etc., the 7D is likely to be more ideal. If you are a JPEG shooter who want's relatively finished images straight out of the camera, the 70D might be a better choice. The 7D is a bit more durable and solid feeling camera. The 70D has a slightly different control layout (no "joystick" for example... it uses a multi-switch instead). You might want to go to a store and handle both 7D and 70D, to help you decide.
Either 7D or 70D will be a big upgrade from your 30D and D30 days, I can assure you. There will be some learning curve with them, a lot of new features to get accustomed to and tweak to your own preferences. But the end results will be quite good, even if not purely the best IQ available.
Oh, and I do suspect the 7D will be replaced with a Mark II model in the not-too-distant future... But it's anyone's guess when that might be (my guess is Spring 2014). It's even murkier what changes it might see. Some things are predictable, while others aren't. The 70D was just recently introduced and is likely to be offered for at least 18 months or longer.